2.8 Viewport and Render Preview
It is because LookDev don't care about lighting, materials,etc. It just gives the quick view of how render will look.
So first of all add a lamp to viewport by Shift+A and click Lamp>Sun, Grab it by pressing G and take it on top of your object.
Edit:
I missed out to look the rendering engine you have selected, It should be Cycles. Change it to Cycles by going to render settings and click on Rendering engine dropdown and select Cycles.


  EEVEE is not capable to show reflections and stuffs.